Don't create unexpected OOPIFs in --isolate-extensions.

content/browser/frame_host/render_frame_host_manager.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/frame_host/render_frame_host_manager.h"
 
 #include <algorithm>
 #include <utility>
 
 #include "base/command_line.h"
@@ skipping 2301 matching lines @@
 
 RenderFrameHostImpl* RenderFrameHostManager::UpdateStateForNavigate(
     const GURL& dest_url,
     SiteInstance* source_instance,
     SiteInstance* dest_instance,
     ui::PageTransition transition,
     bool dest_is_restore,
     bool dest_is_view_source_mode,
     const GlobalRequestID& transferred_request_id,
     int bindings) {
-  // Don't swap for subframes unless we are in --site-per-process.  We can get
-  // here in tests for subframes (e.g., NavigateFrameToURL).
-  if (!frame_tree_node_->IsMainFrame() &&
-      !SiteIsolationPolicy::AreCrossProcessFramesPossible()) {
-    return render_frame_host_.get();
+  if (!frame_tree_node_->IsMainFrame()) {
+    // Don't swap for subframes unless we are in an OOPIF-enabled mode.  We can
+    // get here in tests for subframes (e.g., NavigateFrameToURL).
+    if (!SiteIsolationPolicy::AreCrossProcessFramesPossible())
+      return render_frame_host_.get();
+
+    // If we are in an OOPIF mode that only applies to some sites, only swap if
+    // the policy determines that a transfer would have been needed.  We can get
+    // here for session restore.

[ncarter (slow), 2015/12/08 22:16:17]

Maybe move these 3 comment lines down to just before IsRendererTransferNeeded?

+    // Note that if dest_url is a unique origin like about:blank, then the need

[ncarter (slow), 2015/12/08 22:16:17]

drop "Note that"

+    // for a swap is determined by the source_instance.
+    GURL resolved_url = dest_url;
+    if (url::Origin(resolved_url).unique()) {
+      // If there is no source_instance for a unique origin, then we should
+      // avoid a process swap.
+      if (!source_instance)
+        return render_frame_host_.get();
+
+      // Use source_instance to determine if a swap is needed.
+      resolved_url = source_instance->GetSiteURL();
+    }
+    if (!IsRendererTransferNeededForNavigation(render_frame_host_.get(),
+                                               resolved_url)) {
+      DCHECK(!dest_instance ||
+             dest_instance == render_frame_host_->GetSiteInstance());
+      return render_frame_host_.get();
+    }
   }
 
   SiteInstance* current_instance = render_frame_host_->GetSiteInstance();
   scoped_refptr<SiteInstance> new_instance = GetSiteInstanceForNavigation(
       dest_url, source_instance, dest_instance, nullptr, transition,
       dest_is_restore, dest_is_view_source_mode);
 
   // If we are currently navigating cross-process to a pending RFH for a
   // different SiteInstance, we want to get back to normal and then navigate as
   // usual.  We will reuse the pending RFH below if it matches the destination
@@ skipping 323 matching lines @@
 int RenderFrameHostManager::GetOpenerRoutingID(SiteInstance* instance) {
   if (!frame_tree_node_->opener())
     return MSG_ROUTING_NONE;
 
   return frame_tree_node_->opener()
       ->render_manager()
       ->GetRoutingIdForSiteInstance(instance);
 }
 
 }  // namespace content